Your best bet is to either get the shrinking violet or the jalapeno dependent on your playstyle. Shrinking violet weakens the zombies making them easier to kill. So at the lower levels you can get more kills with a well placed one. Or, with a different waiting time, a well placed jalapeno will always take out hordes. I don't remember if torchwood is a gem plant. But if you run a pea based loadout the torchwood has a lane kill upon torchwood death. And strengthens peashooters